With the development of an AV system provided in a vehicle, more and more attention is paid to the sound in the vehicle. For example, the sound of a portable device such as a mobile terminal, a PMP, an MP3 player, etc., is output from a speaker through a wireless and wired connection means such as Bluetooth, AUX, etc. In particular, active research is being conducted to control the sound output from the speaker in the vehicle in accordance with a location in the vehicle (a rider's position).
A sound control technology includes, for example, a sound field reproduction method, an active noise control method which decreases a sound volume of a space by using a plurality of active sound sources, a method for changing an interval between the sound sources arranged in a specific shape, and a method for increasing a sound power which is radiated at a specific angle by changing a time delay between the sound sources and the magnitude of the sound input.
However, it is difficult to apply a mathematical solution for a specific sound source array to any sound source. For this reason, optimization research has been conducted to obtain a maximum directionality in a particular direction through the assumption of any sound source array. However, this research has assumed only any sound source array and is not suitable to be applied to a common listening space having radiation forms of various sound sources, sound reflection, and sound absorption.
Furthermore, U.S. Pat. No. 5,802,190 (Title of the invention: Linear speaker array) discloses a technology for controlling indirect characteristics such as directionality by using a limited assumption which ignores the distance to the listener or reflection, etc. U.S. Pat. No. 5,910,990 (Title of the invention: Apparatus and method for automatic equalization of personal multi-channel audio system) discloses a method for reproducing a signal without distortion by using transfer function.
Also, Korean Patent Application No. 10-2008-0125309 (Title of the invention: Directional sound generating apparatus and method) proposes a method for radiating a sound to a specific zone. However, it includes content that the sound is focused on the specific zone by disposing high directional speakers, etc.
The above-mentioned documents have a problem in that it is difficult to control a zone on which the sound is intended to be focused in the environment, for example, a vehicle, where the locations of the speakers are fixed. That is, a hardware-based change is necessarily required because the sound cannot be focused on the specific zone by using existing mounted speakers.
As such, the conventional method for controlling the sound in a space by using a plurality of the sound sources simply changes the time delay between the sound sources and the magnitude of the sound input, and only changes the directionality of the sound source by using a restricted type of the sound source array, without considering a rider's position in the vehicle.
In particular, in a condition where a driver makes a call frequently through Bluetooth while driving, other riders in the vehicle do not need to hear the call contents, so that it is necessary that the other calling party's voice output from the speaker should be focused on the driver. However, the above-mentioned method cannot change the location of the speaker in the vehicle and thus cannot be applied to existing vehicles.
Furthermore, when an alarm sound is output from a navigation apparatus during the playing of music through the AV system in the vehicle, there is a case where the music and the alarm sound from the navigation apparatus are simultaneously output from the same speaker. Here, there is a need to control the position where the output of the music is focused and the position where the alarm sound of the navigation apparatus is focused.
As such, there are high technical requirements for controlling the locations of a variety of sounds output in the vehicle.